The present discussion relates to industrial process control monitoring systems. More particularly, the present discussion relates to field devices in process control systems that include wireless communication capability.
In industrial settings, control systems are used to monitor and control industrial and chemical processes and the like. Typically, the control systems perform these functions using field devices that are distributed at key locations in the industrial process and are coupled to the control circuitry in the control room by a process control loop. The term “field device” refers to any device that performs a function in a distributed control or process monitoring system, including devices used in the measurement, control, and monitoring of industrial processes.
Some field devices include a transducer. A transducer, for the purposes of this discussion, is understood to mean either a device that generates an output signal based on a physical input or that generates a physical output based on an input signal. Typically, a transducer transforms an input into an output having a different form. Some examples of transducers include pressure sensors, thermistors, thermocouples, strain gauges, flow transmitters, positioning devices, actuators, solenoids, and indicator lights.
Generally, field devices are characterized by their ability to operate in environments in which the field devices may be exposed to environmental stresses such as temperature, humidity and pressure. In addition, field devices must often withstand exposure to corrosive, hazardous and/or even explosive environments. Further, such devices may also be required operate in the presence of vibration and/or electromagnetic interference. For protection in such potentially harsh environments, field devices often include a rugged housing, often made of metal. Not only do field devices have to operate in potentially harsh environments, they often have to make sensitive measurements. Thus, the circuitry within particular field devices often requires sensitive components to make accurate measurements.
Field devices can also include circuitry for communicating over a process control loop with other monitoring or control devices such as, for example, other installed field devices, hand held tools, or equipment that may be remotely located, for example, in a process control room. Data transmitted over the process control loop can be transmitted in either an analog or digital format. Analog field devices are often connected to other devices via two-wire process control current loops. For example, a number of field devices can be connected to a process control room via a single two-wire control loop. In addition to, or alternatively, the process control loop can carry digital signals used for communication between devices. Field devices that communicate digitally can respond to and communicate selectively with selected devices. Further, such devices can provide additional signaling such as diagnostics and/or alarms.
Some field devices have incorporated wireless technologies to facilitate communication with other monitoring and control devices in addition to or instead of the two-wire communication loop described above. Wireless communication technologies provide the advantage of simplifying field device implementation because field devices that do not rely on wired communication need not have wires provided to them. Some field devices have an attached antenna that is in communication with wireless communication circuitry located with the field device to boost the transmitted signals.